The present invention relates to a motor vehicle, an indicating device and an operating method.
In this case the motor vehicle comprises at least one drive unit, which may be disengaged from the rest of the drive train by, for example, a suitable clutch. The object of the invention is to indicate to the driver when he is in a running state, in which the vehicle would continue to drive with the same longitudinal acceleration, even if the clutch between the drive unit and the rest of the drive train were disengaged. This running state is called “coasting” and makes possible an operating mode that saves energy by switching off the drive unit when the clutch is disengaged or by operating the drive unit at least at a reduced speed, normally idling speed.
In principle, three different drive states can be distinguished in a motor vehicle that is, accelerating, unpowered driving (“coasting”) and decelerating. It is known that coasting is the most energy efficient mode of operation, if at the same time the drive motor is disengaged from the drive train and is switched off or at least is operated at the lowest possible speed. In principle, this operating mode may be used in any conventional vehicle. In vehicles with a manually operated transmission, this operating mode is initiated by stepping on the clutch pedal and releasing the drive pedal. In vehicles with automatic transmission, this mode can be initiated by shifting into the driving position N, instead of actuating the clutch pedal. Vehicles with a hybrid drive will use this operating mode automatically, as often as possible. Yet in this context there are two problems. At any driving speed the unpowered state is a narrow range of the vehicle longitudinal acceleration—more precisely, only a single operating point, characterized by a position of the drive pedal for each engine speed. For this reason the energy saving coasting mode in the case of an automatic activation can be activated only very infrequently, if no influence is to be put on the driver's desired longitudinal acceleration.
Of course, hybrid vehicles have the possibility of covering a certain range of the longitudinal deceleration by means of the additional electric motor when the internal combustion engine is switched off. Yet, even recuperation and then use of the recuperated energy is significantly less efficient than coasting, since during coasting the kinetic energy is maintained and is reduced only by unavoidable driving resistances. However, in the case of recuperation only approximately 50% of the recuperated energy or less can be used again at a later date for accelerating. Therefore, even in the case of hybrid vehicles it is logical to use the energy efficient coasting mode as often as possible. If the driver performs the activation, there is the problem that it is difficult for him to detect this state, so that, on the one hand, he will not often use the energy saving operating mode and, on the other hand, he will activate from time to time the energy saving coasting mode only to ascertain then that the vehicle accelerates unintentionally with more or less speed than intended.
If the coasting state can be indicated to the driver, then he is in a position to induce or maintain depending on the driving situation this state by changing his manner of driving. That is, he can dispense with accelerating slightly more or less than he would have without any information about the relationships. Therefore, in the case of an automatic activation of the energy efficient coasting mode, this operating mode may be active significantly more often similarly when activated by the driver, since otherwise he would not even take the opportunity to activate without the influencing of the longitudinal dynamics.